The maintenance of cell populations within an organism is governed by the cellular processes of cell division and programmed cell death. Within normal cells, the cellular events associated with the initiation and completion of each process is highly regulated. In proliferative disease such as cancer, one or both of these processes may be perturbed. For example, a cancer cell may have lost its regulation (checkpoint control) of the cell division cycle through either the overexpression of a positive regulator or the loss of a negative regulator, perhaps by mutation.
Alternatively, a cancer cell may have lost the ability to undergo programmed cell death through the overexpression of a negative regulator. Hence, there is a need to develop new chemotherapeutic drugs that will restore the processes of checkpoint control and programmed cell death to cancerous cells.
One approach to the treatment of human cancers is to target a protein that is essential for cell cycle progression. In order for the cell cycle to proceed from one phase to the next, certain prerequisite events must be completed. There are checkpoints within the cell cycle that enforce the proper order of events and phases. One such checkpoint is the spindle checkpoint that occurs during the metaphase stage of mitosis. Small molecules that target proteins with essential functions in mitosis may initiate the spindle checkpoint to arrest cells in mitosis. Of the small molecules that arrest cells in mitosis, those which display anti-tumor activity in the clinic also induce apoptosis, the morphological changes associated with programmed cell death. An effective chemotherapeutic for the treatment of cancer may thus be one which induces checkpoint control and programmed cell death. Unfortunately, there are few compounds available for controlling these processes within the cell. Most compounds known to cause mitotic arrest and apoptosis act as tubulin binding agents. These compounds alter the dynamic instability of microtubules and indirectly alter the function/structure of the mitotic spindle thereby causing mitotic arrest. Because most of these compounds specifically target the tubulin protein which is a component of all microtubules, they may also affect one or more of the numerous normal cellular processes in which microtubules have a role. Hence, there is also a need for small molecules that more specifically target proteins associated with proliferating cells.
Eg5 is one of several kinesin-like motor proteins that are localized to the mitotic spindle and known to be required for formation and/or function of the bipolar mitotic spindle. Recently, there was a report of a small molecule that disturbs bipolarity of the mitotic spindle (Mayer, T. U. et. al. 1999. Science 286(5441) 971-4, herein incorporated by reference). More specifically, the small molecule induced the formation of an aberrant mitotic spindle wherein a monoastral array of microtubules emanated from a central pair of centrosomes, with chromosomes attached to the distal ends of the microtubules. The small molecule was dubbed “monastrol” after the monoastral array. This monoastral array phenotype had been previously observed in mitotic cells that were immunodepleted of the Eg5 motor protein. This distinctive monoastral array phenotype facilitated identification of monastrol as a potential inhibitor of Eg5. Indeed, monastrol was further shown to inhibit the Eg5 motor-driven motility of microtubules in an in vitro assay. The Eg5 inhibitor monastrol had no apparent effect upon the related kinesin motor or upon the motor(s) responsible for golgi apparatus movement within the cell. Cells that display the monoastral array phenotype either through immunodepletion of Eg5 or monastrol inhibition of Eg5 arrest in M-phase of the cell cycle. However, the mitotic arrest induced by either immunodepletion or inhibition of Eg5 is transient (Kapoor, T. M., 2000. J Cell Biol 150(5) 975-80). Both the monoastral array phenotype and the cell cycle arrest in mitosis induced by monastrol are reversible. Cells recover to form a normal bipolar mitotic spindle, to complete mitosis and to proceed through the cell cycle and normal cell proliferation. These data suggest that a small molecule inhibitor of Eg5 which induced a transient mitotic arrest may not be effective for the treatment of cancer cell proliferation. Nonetheless, the discovery that monastrol causes mitotic arrest is intriguing and hence there is a need to further study and identify compounds which can be used to modulate the Eg5 motor protein in a manner that would be effective in the treatment of human cancers. There is also a need to explore the use of these compounds in combination with other antineoplastic agents.
VEGF (also known as vascular permeability factor, VPF) is a multifunctional cytokine that stimulates angiogenesis, epithelial cell proliferation, and endothelial cell survival. VEGF can be produced by a wide variety of tissues, and its overexpression or aberrant expression can result in a variety disorders, including cancers and retinal disorders such as age-related macular degeneration and other angiogenic disorders.
Recently, double-stranded RNA molecules (dsRNA) have been shown to block gene expression in a highly conserved regulatory mechanism known as RNA interference (RNAi). WO 99/32619 (Fire et al.) discloses the use of a dsRNA of at least 25 nucleotides in length to inhibit the expression of genes in C. elegans. dsRNA has also been shown to degrade target RNA in other organisms, including plants (see, e.g., WO 99/53050, Waterhouse et al.; and WO 99/61631, Heifetz et al.), Drosophila (see, e.g., Yang, D., et al., Curr. Biol. (2000) 10:1191-1200), and mammals (see WO 00/44895, Limmer; and DE 101 00 586.5, Kreutzer et al.). This natural mechanism has now become the focus for the development of a new class of pharmaceutical agents for treating disorders that are caused by the aberrant or unwanted regulation of a gene.
Despite significant advances in the field of RNAi and advances in the treatment of pathological processes mediated by Eg5 expression, there remains a need for an agent that can selectively and efficiently silence the Eg5 gene using the cell's own RNAi machinery that has both high biological activity and in vivo stability, and that can effectively inhibit expression of a target Eg5 gene for use in treating pathological processes mediated by Eg5 expression.